See Chapter 6 of the iMQ 2.0 Adminstrator's Guide:
(http://docs.sun.com/db?p=/doc/816-5909-10)
You can use jmqcmd to manage the broker state. To
shutdown the broker you could do the following:
% jmqcmd shutdown bkr -u admin -p admin
This would cleanly shutdown the broker running on
the localhost and default port.
Chris